Brief communication: <scp>CMIP6</scp> does not suggest any atmospheric blocking increase in summer over Greenland by 2100

Delhasse, Alison; Hanna, Edward; Kittel, Christoph; Fettweis, Xavier

doi:10.1002/joc.6977

Cited by 25 publications

(36 citation statements)

References 41 publications

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“…Fully coupled CMIP6 simulations (i.e., with an active ocean and sea ice component) show decreases in blocking over Greenland (Delhasse et al 2021), in opposition to our results presented here. We hypothesize that cooling of sea surface temperatures in the North Atlantic (Sellevold and Vizcaino 2020), due to the projected slowdown of the North Atlantic Meridional Overturning Circulation in the fully coupled models, causes the decrease in Greenland blocking.…”

Section: Discussioncontrasting

confidence: 99%

“…7 b), as the winds affect the amount of moisture transfer over the ice sheet. Further, this circulation anomaly is similar to the circulation anomaly associated with the Greenland blocking index (Davini et al 2012 ; Hanna et al 2015 , 2018 ). However, the present-day GBI-related anomaly is approximately 6 stronger than the circulation anomaly found here (Hanna et al 2016 ).…”

Section: Resultssupporting

confidence: 76%

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Influence of Arctic sea-ice loss on the Greenland ice sheet climate

2021

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The Arctic is the region on Earth that is warming the fastest. At the same time, Arctic sea ice is reducing while the Greenland ice sheet (GrIS) is losing mass at an accelerated pace. Here, we study the seasonal impact of reduced Arctic sea ice on GrIS surface mass balance (SMB), using the Community Earth System Model version 2.1 (CESM2), which features an advanced, interactive calculation of SMB. Addressing the impact of sea-ice reductions on the GrIS SMB from observations is difficult due to the short observational records. Also, signals detected using transient climate simulations may be aliases of other forcings. Here, we analyze dedicated simulations from the Polar Amplification Model Intercomparison Project with reduced Arctic sea ice and compare them with preindustrial sea ice simulations while keeping all other forcings constant. In response to reduced sea ice, the GrIS SMB increases in winter due to increased precipitation, driven by the more humid atmosphere and increasing cyclones. In summer, surface melt increases due to a warmer, more humid atmosphere providing increased energy transfer to the surface through the sensible and latent heat fluxes, which triggers the melt-albedo feedback. Further, warming occurs throughout the entire troposphere over Baffin Bay. This deep warming results in regional enhancement of the 500 hPa geopotential heights over the Baffin Bay and Greenland, increasing blocking and heat advection over the GrIS’ surface. This anomalous circulation pattern has been linked to recent increases in the surface melt of the GrIS.

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Section: Discussioncontrasting

confidence: 99%

Section: Resultssupporting

confidence: 76%

Influence of Arctic sea-ice loss on the Greenland ice sheet climate

2021

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“…S1b in the Supplement), once integrated over the whole ice sheet (see Table S1 in the Supplement), these anomalies compensate for each other and the SMB components as well as the solar radiation compare very well with the ones from MAR forced by ERA5. Furthermore, Delhasse et al (2021) showed that CMIP6 models do not suggest any change in general circulation in summer. This suggests that the pattern of the present-day runoff anomalies should remain unchanged through the MAR simulation and then that the excess of runoff along the south-west margin should continue to compensate for the lack of runoff in the north-east.…”

Section: Modelsmentioning

confidence: 99%

Brief communication: Reduction in the future Greenland ice sheet surface melt with the help of solar geoengineering

et al. 2021

Self Cite

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Abstract. The Greenland Ice Sheet (GrIS) will be losing mass at an accelerating pace throughout the 21st century, with a direct link between anthropogenic greenhouse gas emissions and the magnitude of Greenland mass loss. Currently, approximately 60 % of the mass loss contribution comes from surface melt and subsequent meltwater runoff, while 40 % are due to ice calving. In the ablation zone covered by bare ice in summer, most of the surface melt energy is provided by absorbed shortwave fluxes, which could be reduced by solar geoengineering measures. However, so far very little is known about the potential impacts of an artificial reduction in the incoming solar radiation on the GrIS surface energy budget and the subsequent change in meltwater production. By forcing the regional climate model MAR with the latest CMIP6 shared socioeconomic pathways (SSP) future emission scenarios (SSP245, SSP585) and associated G6solar experiment from the CNRM-ESM2-1 Earth system model, we estimate the local impact of a reduced solar constant on the projected GrIS surface mass balance (SMB) decrease. Overall, our results show that even in the case of a low-mitigation greenhouse gas emissions scenario (SSP585), the Greenland surface mass loss can be brought in line with the medium-mitigation emissions scenario (SSP245) by reducing the solar downward flux at the top of the atmosphere by ∼ 40 W/m2 or ∼ 1.5 % (using the G6solar experiment). In addition to reducing global warming in line with SSP245, G6solar also decreases the efficiency of surface meltwater production over the Greenland ice sheet by damping the well-known positive melt–albedo feedback. With respect to a MAR simulation where the solar constant remains unchanged, decreasing the solar constant according to G6solar in the MAR radiative scheme mitigates the projected Greenland ice sheet surface melt increase by 6 %. However, only more constraining geoengineering experiments than G6solar would allow us to maintain a positive SMB until the end of this century without any reduction in our greenhouse gas emissions.

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“…However, the total yearly melt rates match well with those of MAR over the period 1958-2019 and on this timescale the skill of the model is comparable to the dEBM (Krebs-Kanzow et al, 2020). The exception of the extreme melt in the years 2012 and 2019, where dEBM-simple clearly underestimates melt rates, are related to changes in cloud cover or blocking events (Delhasse et al, 2021;Hanna et al, 2014;Hofer et al, 2017), which are not captured by the parameterization of the transmissivity of the atmosphere.…”

Section: Implementation and Validationmentioning

confidence: 59%

Impact of the melt-albedo feedback on the future evolution of the Greenland Ice Sheet with PISM-dEBM-simple

Zeitz

Reese

Beckmann

et al. 2021

Preprint

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Abstract. Surface melting of the Greenland Ice Sheet contributes a large amount to current and future sea-level rise. Increased surface melt, algae growth, debris, and dust deposition lower the reflectivity of the ice surface and thereby increase melt rates: the so-called melt-albedo feedback describes this potentially self-sustaining increase in surface melting. Here we present a simplified version of the diurnal Energy Balance Model (dEBM-simple) which is implemented as a surface melt module in the Parallel Ice Sheet Model (PISM). dEBM-simple is a modification of diurnal Energy Balance Model (dEBM), a surface melt scheme of intermediate complexity useful for simulations over centennial to multi-millennial timescales. dEBM-simple is computationally efficient, suitable for standalone ice-sheet modeling and includes a simple representation of the melt-albedo feedback. Using dEBM-simple and PISM, we find that this feedback increases ice loss until 2300 through surface warming by 60 % for the high-emission scenario RCP8.5. With an increase of 90 %, the effect is more pronounced for lower surface warming under RCP2.6. Furthermore, assuming an immediate darkening of the ice surface over all summer months, we estimate an upper bound for this effect to be +70 % in the RCP8.5 scenario and a more than fourfold increase under RCP2.6. With dEBM-simple implemented in PISM, we find that the melt-albedo feedback is an essential contributor to mass loss in dynamic simulations of the Greenland Ice Sheet under future warming.

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Brief communication: CMIP6 does not suggest any atmospheric blocking increase in summer over Greenland by 2100

Cited by 25 publications

References 41 publications

Influence of Arctic sea-ice loss on the Greenland ice sheet climate

Influence of Arctic sea-ice loss on the Greenland ice sheet climate

Brief communication: Reduction in the future Greenland ice sheet surface melt with the help of solar geoengineering

Impact of the melt-albedo feedback on the future evolution of the Greenland Ice Sheet with PISM-dEBM-simple

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